Some widely publicised papers suggesting that fishes and fish catches will be smaller in the future are based on false assumptions

Some models show that fish will have a smaller size in the future due to climate changes. Three researchers are now pointing out that these models are built on false assumptions.

Two physiologists, Sjannie Lefevre and Göran E. Nilsson, from the Department of Biosciences, the University of Oslo, have together with a colleague, David J. McKenzie at the University of Montpellier, published a paper in Global Change Biology this week showing that some highly cited and publicised modelling studies are based on erroneous physiological principles and facts. These models are suggesting that fishes will become smaller in the warmer climate expected in the future. The authors behind these modelling studies may be prominent fisheries biologists and modellers, but unfortunately some fundamental assumptions made in the models are simply incorrect, says Sjannie Lefevre. For once, they got the geometrical principles guiding the surface area of fish gills completely wrong, and they also make the unfounded assumption that the capacity of fish to take up oxygen from the water limits their ability to grow. It is troublesome that these inaccurate assumptions have been allowed to go unnoticed by fish physiologists, but they are partly hidden in the formulas used and in some obscure statements made in these papers. Lefevre, McKenzie and Nilsson say that they do not deny the possibility that fishes may become smaller in the warmer future, although there is currently not much firm evidence for this, but any such predictions must be based on verified mechanisms and experimental evidence.

La Niña conditions were observed during October, with negative sea surface temperature (SST) anomalies in early November stretching across most of the eastern and central equatorial Pacific Ocean [Fig. 1]. With the exception of the Niño1+2 region, the Niño region indices remained negative over the last month, with the latest weekly value of the Niño-3.4 index at -0.8°C [Fig. 2]. The upper-ocean heat content also remained below average during October [Fig. 3], reflecting below-average temperatures at depth [Fig. 4]. Convection was suppressed over the central tropical Pacific and enhanced over Indonesia [Fig. 5]. The lower-level easterly winds were weakly enhanced near and west of the International Date Line, and anomalously westerly upper-level winds were mainly west of the International Date Line. Overall, the ocean and atmosphere system reflected weak La Niña conditions.

European seasonal mortality and influenza incidence due to winter temperature variabilityRecent studies have vividly emphasized the lack of consensus on the degree of vulnerability (see ref. 1) of European societies to current and future winter temperatures. Here we consider several climate factors, influenza incidence and daily numbers of deaths to characterize the relationship between winter temperature and mortality in a very large ensemble of European regions representing more than 400 million people. Analyses highlight the strong association between the year-to-year fluctuations in winter mean temperature and mortality, with higher seasonal cases during harsh winters, in all of the countries except the United Kingdom, the Netherlands and Belgium. This spatial distribution contrasts with the well-documented latitudinal orientation of the dependency between daily temperature and mortality within the season. A theoretical framework is proposed to reconcile the apparent contradictions between recent studies, offering an interpretation to regional differences in the vulnerability to daily, seasonal and long-term winter temperature variability. Despite the lack of a strong year-to-year association between winter mean values in some countries, it can be concluded that warmer winters will contribute to the decrease in winter mortality everywhere in Europe.

Human-induced greening of the northern extratropical land surfaceSignificant land greening in the northern extratropical latitudes (NEL) has been documented through satellite observations during the past three decades1, 2, 3, 4, 5. This enhanced vegetation growth has broad implications for surface energy, water and carbon budgets, and ecosystem services across multiple scales6, 7, 8. Discernible human impacts on the Earth’s climate system have been revealed by using statistical frameworks of detection–attribution9, 10, 11. These impacts, however, were not previously identified on the NEL greening signal, owing to the lack of long-term observational records, possible bias of satellite data, different algorithms used to calculate vegetation greenness, and the lack of suitable simulations from coupled Earth system models (ESMs). Here we have overcome these challenges to attribute recent changes in NEL vegetation activity. We used two 30-year-long remote-sensing-based leaf area index (LAI) data sets12, 13, simulations from 19 coupled ESMs with interactive vegetation, and a formal detection and attribution algorithm14, 15. Our findings reveal that the observed greening record is consistent with an assumption of anthropogenic forcings, where greenhouse gases play a dominant role, but is not consistent with simulations that include only natural forcings and internal climate variability. These results provide the first clear evidence of a discernible human fingerprint on physiological vegetation changes other than phenology and range shifts11.

Under ice habitats for Antarctic krill larvae: Could less mean more under climate warming?Overwintering of larvae underneath Antarctic pack ice is a critical stage in the life cycle of Antarctic krill. However, there are no circumpolar assessments of available habitat for larval krill, making it difficult to evaluate how climate change may impact this life stage. We use outputs from a circumpolar sea ice model, together with a set of simple assumptions regarding key habitat features, to identify possible regions of larval krill habitat around Antarctica during winter. We assume that the location and suitability of habitat is determined by both food availability and three-dimensional complexity of the sea ice. A comparison of the combined area of these regions under current conditions with a warm climate scenario indicates that while total areal sea ice extent decreases, there is a consistently larger area of potential larval krill habitat under warm conditions. These findings suggest that decreases in sea ice extent may not necessarily be detrimental for krill populations.

New research shows that human pollution of the atmosphere with acid is now almost back to the level that it was before the pollution started with industrialisation in the 1930s. The results come from studies of the Greenland ice sheet and are published in the scientific journal, Environmental Science and Technology.

The Greenland ice sheet is a unique archive of the climate and atmospheric composition far back in time. The ice sheet is made up of snow that falls and never melts, but rather remains year after year and is gradually compressed into ice. By drilling ice cores down through the kilometre-thick ice sheet, the researchers can analyse every single annual layer, which can tell us about past climate change and concentration of greenhouse gases and pollutants in the atmosphere.

Acid in the atmosphere can come from large volcanic eruptions and manmade emissions from industry. You can measure acidity in the ice by simply passing an instrument that can measure conductivity over the ice core. If there is a high level of acidity, the measurement turns out and it works great for measuring the climate of the past all the way back to the last interglacial period 125,000 years ago. But if you want to measure atmospheric acidity for the last 100 years, it is more difficult as the annual layers are located in the uppermost 60 metres and there the ice is more porous as it has not yet been compressed into hard ice.

Measures pollution from year to year

But the last 100 years are interesting for climate researchers as it is the period where we have had massive pollution of the atmosphere from industrialisation, vehicle use and people’s energy consuming lifestyles.

“We have therefore developed a new method that can directly measure the acidity of the ice using a spectrometer. We have an ice rod that is cut along the length of the ice core. This ice core rod is slowly melted and the meltwater runs into a laboratory where they take a lot of chemical measurements. With our new method you can also measure the acidity, that is to say, we measure the pH value and this is seen when the water changes colour after the addition of a pH dye. We can directly see the fluctuations from year to year,” explains Helle Astrid Kjær, postdoc in the Centre for Ice and Climate at the Niels Bohr Institute, University of Copenhagen.

For many years, there has been a quest to solve the problem of measuring acidity in the porous annual layers of the ice and now scientists from the Niels Bohr Institute have succeeded. The method is a Continuous Flow Analyses or CFA method and it was originally invented in Switzerland, but Helle Astrid Kjær has spearheaded the further development of the system so it can also measure acid.

Distinguishes between natural and manmade sources

In addition to being able to measure the pH value more accurately using the new method, the CFA system can also distinguish whether the emissions come from volcanic eruptions, large forest fires or industry. The researchers can therefore filter out both volcanic eruptions and forest fires in the assessment of industrial pollution and the new results are revolutionary.

“We can see that the acid pollution in the atmosphere from industry has fallen dramatically since manmade acid pollution took off in the 1930s and peaked in the 1960s and 70s. In the 1970s, both Europe and the United States adopted the ‘The clean air act amendments’, which required filters in factories, thus reducing acid emissions and this is what we can now see the results of. The pollution of acid in the atmosphere is now almost down to the level it was before the pollution really took off in the 1930s, explains Helle Astrid Kjær.

The new pH method has already been used on ice cores from Greenland and Antarctica by research teams from New Zealand, the United States and Denmark.

Wetlands and agriculture, not fossil fuels could be causing a global rise in methane

Research published today in the American Geophysical Union’s journal Global Biogeochemical Cycles shows that recent rises in levels of methane in our atmosphere is being driven by biological sources, such as swamp gas, cow burps, or rice fields, rather than fossil fuel emissions.

Atmospheric methane is a major greenhouse gas that traps heat in our atmosphere, contributing to global warming. Its levels have been growing strongly since 2007, and in 2014 the growth rate of methane in the atmosphere was double that of previous years, largely driven by biological sources as opposed to fossil fuel emissions.

Conventional wisdom refuted

The study, led by researchers at Royal Holloway, University of London shows that methane emissions have been increasing, particularly in the tropics. Researchers discovered that biological sources, such as methane emissions from swamps, make up the majority of increase. “Our results go against conventional thinking that the recent increase in atmospheric methane must be caused by increased emissions from natural gas, oil, and coal production. Our analysis of methane’s isotopic composition clearly points to increased emissions from microbial sources, such as wetlands or agriculture” said lead author Euan Nisbet from Royal Holloway, University of London’s Department of Earth Sciences.

Methane growth rate doubles

Professor Nisbet says “Atmospheric methane is one of the most potent greenhouses gases. Methane increased through most of the 20th century, driven largely by leaks from the gas and coal industries.” He continued, “At the beginning of this century it appeared that the amount of methane in the air was stabilising, butsince 2007 the levels of methane have started growing again. The year 2014 was extreme, with the growth rate doubling, and large increases seen across the globe.”

Tropics identified as key source

The research shows that in recent years, the increase in methane has been driven by sharp increases in the tropics, in response to changing weather patterns. It is possible that the natural processes that remove methane from the atmosphere have slowed down, but it is more likely that there’s been an increase of methane emission instead, especially from the hot wet tropics. Professor Nisbet and his team, together with the US The National Oceanic and Atmospheric Administration (NOAA), have been looking at measurements and samples of air taken from places like Alert in the Canadian Arctic; Ascension, a UK territory in the South Atlantic; Cape Point, South Africa.

International collaboration leads to new conclusions

The research has been carried out by an international team of atmospheric scientists, led by Euan Nisbet, from Royal Holloway, University of London. Ed Dlugokencky, from the NOAA, Martin Manning from Victoria University, Wellington, New Zealand and a team from the University of Colorado’s Institute of Arctic and Alpine Research, led by Jim White, have been working with collaborators from the UK, France, Canada, and South Africa.

Europe once had widespread malaria, but today it is free from endemic transmission. Changing land use, agricultural practices, housing quality, urbanization, climate change, and improved healthcare are among the many factors thought to have played a role in the declines of malaria seen, but their effects and relative contributions have rarely been quantified.

Methods

Spatial datasets on changes in climate, wealth, life expectancy, urbanization, and land use trends over the past century were combined with datasets depicting the reduction in malaria transmission across 31 European countries, and the relationships were explored. Moreover, the conditions in current malaria-eliminating countries were compared with those in Europe at the time of declining transmission and elimination to assess similarities.

Results/conclusions

Indicators relating to socio-economic improvements such as wealth, life expectancy and urbanization were strongly correlated with the decline of malaria in Europe, whereas those describing climatic and land use changes showed weaker relationships. Present-day malaria-elimination countries have now arrived at similar socio-economic indicator levels as European countries at the time malaria elimination was achieved, offering hope for achievement of sustainable elimination.

… “The debate over climate phenomenon is over scientifically and environmentally,” said Ban, adding that the influence of climate change deniers or skeptics has waned. “It is affecting our day-to-day life,” Ban said, at a new conference ahead of a G20 summit in the eastern Chinese city of Hangzhou. …

Word of mouth from nomadic herders led Lucas Silva into Tibetan forests and grasslands. What his team found was startling: Rapid forest growth in tune with what scientists had been expecting — but not yet seeing — from climatic changes triggered by rising levels of carbon dioxide.

Actual scientific findings to date have turned up declining growths in many forests in the face of a warming climate. Such had also been the case for Silva, who joined the UO’s Environmental Studies Program and Department of Geography in August [2016]. On the eastern Tibetan Plateau, in an area where it was thought that “climatically induced ecological thresholds had not yet been crossed,” Silva’s team found that the increasing availability of soil nutrients and water from thawing permafrost is stimulating the chemistry of the wood in a species of fir trees. “Our results confirmed the reports of local herders and showed a recent increase in tree growth that has been unprecedented since the year 1760,” Silva said. “These result demonstrate that under a specific set of conditions, forests can respond positively to human-induced changes in climate.” The findings were published in Science Advances, an online, open-access publication of the American Association for the Advancement of Science.

Nomads had reported their observations to study co-author Geng Sun of China’s Chengdu Institute of Biology in Sichuan, China. The research team traveled to the region in eastern Tibet, where they found old-growth forests, smaller patches of trees and trees isolated on the perimeter of the forests. “We wanted to take a long term view of changes in tree growth across this gradient,” Silva said. “To do so, we combined tree-ring measurements with laboratory analyses to look for changes in growth as well as chemical signals of climatic change.” Those techniques provided a window on the history of the area’s tree growth. Dramatic increases in growth have coincided with pulses of tree establishment just outside of the forest range but apparently not yet occurring on a broader regional scale, he said. Growth was rapid between the 1930s and 1960s, but even more accelerated in the last three decades.

Research involving plants grown in controlled laboratory and greenhouse conditions have shown that rising carbon dioxide levels can speed plant growth, but field studies have shown that carbon dioxide-induced growth could not counteract the negative effects of rising temperatures and drought stress in many forest ecosystems. The new findings, the researchers said, suggest that studying the synergy of soil-plant-atmosphere interactions might be the key to understanding the past and predicting future changes in forest productivity and distribution. “Our findings could have important implications for the conservation and management of many different species,” Silva said. “However, it is important to note that we sampled a very small area where forests and grasslands coexist. A comprehensive survey of changes in plant diversity throughout the region has yet to be performed.”

Other co-authors on the paper were William Horwath and Xia Zhu-Barker of the University of California, Davis, Ning Wu from Chengdu Institute of Biology in China and Qianlong Liang from Sichuan University in China. Silva earned his doctorate in 2011 from the University of Guelph in Canada. He received a grant to conduct research in Tibet and began working with Chinese collaborators during a postdoctoral stint at the University of California, Davis, where he eventually landed on the faculty in 2013.

“ These results show that the linear relationship between Arctic sea-ice loss and mid-latitude weather patterns is weak, suggesting that the remote atmospheric response is small compared with the internal variability, or highly nonlinear with respect to the sea-ice area anomalies.”

“Thus, our results do not show evidence of an unusually elongated jet stream associated with Arctic sea-ice loss on a monthly time scale.”

“We have shown using several different metrics that the remote atmospheric response can be non-robust due to internal dynamics alone, and leave diagnosis of mechanisms behind this non-robustness for future studies. “

The robustness of mid-latitude weather pattern changes due to Arctic sea-ice lossThe significance and robustness of the link between Arctic sea-ice loss and changes in mid-latitude weather patterns is investigated through a series of model simulations in Community Atmosphere Model 5.3 with systematically perturbed sea-ice cover in the Arctic. Using a large ensemble of ten sea-ice scenarios and 550 simulations, it is found that prescribed Arctic sea-ice anomalies produce statistically significant changes for certain metrics of the mid-latitude circulation but not for others. Furthermore, the significant mid-latitude circulation changes do not scale linearly with the sea-ice anomalies, and are not present in all scenarios, indicating that the remote atmospheric response to reduced Arctic sea ice can be statistically significant under certain conditions, but is generally non-robust. Shifts in the Northern Hemisphere polar jet stream and changes in the meridional extent of upper-level large-scale waves due to the sea ice perturbations are generally small and not clearly distinguished from intrinsic variability. Reduced Arctic sea ice may favor a circulation pattern that resembles the negative phase of the Arctic Oscillation, and may increase the risk of cold outbreaks in eastern Asia by almost 50 %, but this response is found in only half of the scenarios with negative sea-ice anomalies. In eastern North America the frequency of extreme cold events decreases almost linearly with decreasing sea-ice cover. Our finding of frequent significant anomalies without a robust linear response suggests interactions between variability and persistence in the coupled system, which may contribute to the lack of convergence among studies of Arctic influences on mid-latitude circulation.

Health researchers predict that the transmission of dengue could decrease in a future warmer climate, countering previous projections that climate change would cause the potentially lethal virus to spread more easily.

Hundreds of millions of people are infected with dengue each year, with some children dying in severe cases, and this research helps to address this significant global health problem. Co-lead researcher Associate Professor David Harley from The Australian National University (ANU) said that dengue risk might decrease in the wet tropics of northeast Australia under a high-emissions scenario in 2050, due to mosquito breeding sites becoming drier and less favourable to their survival. “While climate change generally poses a major threat to humanity, it also may reduce the incidence of dengue in some areas,” said Dr Harley, an epidemiology researcher at the ANU Research School of Population Health and ANU Medical School.

The findings are also relevant to other mosquito-borne viruses including Zika because the mosquitoes that carry dengue also transmit the Zika virus. “There is significant concern in countries on the margin of the tropical areas where dengue is mainly found, that with global warming dengue and other mosquito-borne viruses such as Zika will encroach and become common,” Dr Harley said. “Previous projections have suggested that climate change will increase transmission of mosquito-borne diseases globally. “Our work, using a mathematical model based on Queensland conditions, suggests that dengue transmission might decrease with greater warming.”

Dr Harley said the research findings did not suggest authorities could be complacent about climate change’s effect on people’s health. “Generally, health and other impacts of climate warming will be negative in Australia and elsewhere in the world,” he said. “While we could see some reduction in dengue in Far North Queensland in a future warmer climate, the disease is widespread elsewhere in the world where outcomes would be different.” This study was funded by the National Health and Medical Research Council of Australia, and involved ANU, University of South Australia, James Cook University and Australian Red Cross Blood Service. It is published in the latest issue of Epidemiology and Infection.

Future climate warming will likely cause only minor cuts in energy output at most U.S. coal- or gas-fired power plants, a new Duke University study finds. The study — the first of its kind based on real-world data — rebuts recent modeling-based studies that warn rising temperatures will significantly lower the efficiency of power plants’ cooling systems, thereby reducing plants’ energy output. Those studies estimated that plant efficiencies could drop by as much as 1.3 percent for each 1 degree Celsius of climate warming.

“Our data suggest that drops in efficiency at plants with open-loop, or once-through, cooling systems will be a full order of magnitude smaller than this,” said Candise L. Henry, a doctoral student at Duke’s Nicholas School of the Environment. “Reductions at plants with wet-circulation, or closed-loop, systems — which can be identified by their cooling towers — may be even smaller.” “In large part, this is because plant operators are already constantly adjusting operations to optimize plant performance under changing environmental conditions,” she said. “That’s a key consideration the past studies overlooked.”

The new findings do not, however, signal an all’s clear for the power industry, the Duke researchers cautioned. “The impact of future droughts associated with global warming could still significantly affect plant operations and output by reducing the availability of water for cooling,” said Lincoln F. Pratson, Semans-Brown Professor of Earth and Ocean Sciences at Duke.

Henry and Pratson published their findings this month in the peer-reviewed journal Environmental Science & Technology. To conduct their study, they analyzed hourly temperature and humidity data recorded at National Climatic Data Center (NCDC) stations and U.S. Geological Survey river gauges near 39 U.S. coal- or natural-gas-fired power plants over a seven- to 14-year period. By correlating this data with the plants’ hourly heat input and energy output records, obtained through the EPA’s Air Markets Program Data website, they were able to extrapolate how much of each plant’s output was the result of daily and seasonal variations in temperature. “These variations exceed estimates of the average future annual increase in warming under a moderate global warming scenario,” Henry noted, “so we could actually see — based on empirical evidence — how plants’ operations are affected by temperature changes much more dramatic than what is projected to occur.”

To ensure a representative sample, the study included both closed-loop and open-loop plants from the Northeast, Mid-Atlantic, Southeast, Midwest, Deep South, Great Plains and Rocky Mountain regions. Output capacities ranged from less than 500 megawatts up to 3,000 megawatts. The cooling efficiency and energy output of every plant — regardless of location, generating capacity or fuel type — was found to be more resilient to climate warming than previous studies predicted. Plants with closed-loop cooling systems were found to be particularly resilient. “This provides additional rationale for section 316b of the EPA’s Clean Water Act, which requires most electric generators to install closed-loop recirculating systems,” said Pratson. “The EPA enacted section 316b to protect fish, shellfish and other aquatic animals from being pulled into, and harmed or killed in power plants’ cooling water-intake structures,” he noted. “Our study shows it could also provide the added benefit of helping protect the power plants themselves from the impact of climate warming.”

Plants retain more moisture in high carbon dioxide conditions, keeping water on land

As a multiyear drought grinds on in the Southwestern United States, many wonder about the impact of global climate change on more frequent and longer dry spells. As humans emit more carbon dioxide into the atmosphere, how will water supply for people, farms, and forests be affected? A new study from the University of California, Irvine and the University of Washington shows that water conserved by plants under high CO2 conditions compensates for much of the effect of warmer temperatures, retaining more water on land than predicted in commonly used drought assessments. According to the study published this week in the Proceedings of the National Academy of Sciences, the implications of plants needing less water with more CO2 in the environment changes assumptions of climate change impacts on agriculture, water resources, wildfire risk, and plant growth.

The study compares current drought indices with ones that take into account changes in plant water use. Reduced precipitation will increase droughts across southern North America, southern Europe and northeastern South America. But the results show that in Central Africa and temperate Asia — including China, the Middle East, East Asia and most of Russia — water conservation by plants will largely counteract the parching due to climate change. “This study confirms that drought will intensify in many regions in the future,” said coauthor James Randerson, UCI professor of Earth system science. “It also shows that plant water needs will have an important influence on water availability, and this part of the equation has been neglected in many drought and hydrology studies.”

Recent studies have estimated that more than 70 percent of our planet will experience more drought as carbon dioxide levels quadruple from pre-industrial levels over about the next 100 years. But when researchers account for changes in plants’ water needs, this falls to 37 percent, with bigger differences concentrated in certain regions. The reason is that when Earth’s atmosphere holds more carbon dioxide, plants actually benefit from having more of the molecules they need to build their carbon-rich bodies. Plants take in carbon dioxide through tiny openings called stomata that cover their leaves. But as they draw in carbon dioxide, moisture escapes. When carbon dioxide is more plentiful, the stomata don’t need to be open for as long, and so the plants lose less water. The plants thus draw less water from the soil through their roots.

Global climate models already account for these changes in plant growth. But many estimates of future drought use today’s standard indices, like the Palmer Drought Severity Index, which only consider atmospheric variables such as future temperature, humidity and precipitation. “New satellite observations and improvements in our understanding hydrological cycle have led to significant advances in our ability to model changes in soil moisture,” said Randerson. “Unfortunately, using proxy estimates of drought stress can give us misleading results because they ignore well-established principles from plant physiology.”

Planners will need accurate long-term drought predictions to design future water supplies, anticipate ecosystem stresses, project wildfire risks and decide where to locate agricultural fields. “In some sense there’s an easy solution to this problem, which is we just have to create new metrics that take into account what the plants are doing,” said lead author Abigail Swann, a University of Washington assistant professor of atmospheric sciences. “We already have the information to do that; we just have to be more careful about ensuring that we’re considering the role of the plants.”

Is this good news for climate change? Although the drying may be less extreme than in some current estimates, droughts will certainly increase, researchers said, and other aspects of climate change could have severe effects on vegetation. “There’s a lot we don’t know, especially about hot droughts,” Swann said. The same drought at a higher temperature might have more severe impacts, she noted, or might make plants more stressed and susceptible to pests. “Even if droughts are not extremely more prevalent or frequent, they may be more deadly when they do happen,” she said.